Answer:
t = 4 s
Explanation:
As we know that the particle A starts from Rest with constant acceleration
So the distance moved by the particle in given time "t"



Now we know that B moves with constant speed so in the same time B will move to another distance

now we know that B is already 349 cm down the track
so if A and B will meet after time "t"
then in that case


on solving above kinematics equation we have

If you apply a little bit of force, one will move easier than the other since it is lighter.
So impulse is a change in momentum.
Mass*(final velocity - initial velocity)
I dont think you will be able to find the average force with the given info because you need to know the time it takes for the car to slow down.
The answer is 4.0075 x 10^9